As lilacamy says, you likely have one of the so-called "target puffers" from Asia, a small group of very similar species that are all shades of mottled golden-brown with a distinct red or black target-like marking on each side of their flanks. While they vary in size from 8 to about 20 cm, they are all territorial, aggressive fish normally kept alone. At their worst they're extremely nasty fish that bite one another without hesitation. Normal operating procedure is to provide a 100-200 litre aquarium to a single specimen depending on its adult size.
Puffers tend to heal quickly if given good water quality. Antibiotics can certainly be used, but be very careful with anything containing copper or formalin, as both of these are know to irritate, potentially harm, pufferfish.
Cheers, Neale